Porton Down, UK; 20 April 2011: GW Pharmaceuticals plc (AIM: GWP) today announces that the United States Patent and Trademark Office has issued a Notice of Allowance for a patent which protects the use of Sativex® as a treatment for cancer pain.

The patent, entitled “Pharmaceutical Compositions for the Treatment of Pain”, provides an exclusivity period until April 2025. The patent specifically covers a method of treating cancer related pain by administering a combination of the cannabinoids cannabidiol (CBD) and delta-9 tetrahydrocannabinol (THC), the two principal cannabinoids in Sativex®. In addition to this newly granted patent, Sativex® is protected by a number of other patents related to different aspects of the product.

Sativex® is currently in Phase III clinical development as a treatment for cancer pain. Cancer pain represents the lead indication for Sativex® in the United States, where the medicine is partnered with Otsuka Pharmaceutical Co. Ltd.

Dr Geoffrey Guy, GW’s Chairman, said, “The grant of this US patent covering Sativex® as a treatment for cancer pain is part of a broad platform of intellectual property rights which continue to be developed by GW. GW now has 35 patent families as well as other forms of protection such as plant variety rights and proprietary know-how. We believe that this matrix of intellectual property provides GW with a unique position to benefit from the rich promise within the field of cannabinoid therapeutics.”

Sativex® is approved in the UK, Spain, Czech Republic, Canada and New Zealand as a treatment of Multiple Sclerosis spasticity.

Patent abstract: The invention relates to treatment of cancer related pain and constipation. Preferably the subject in need is administered a combination of the cannabinoids cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC). More preferably the cannabinoids are in a predefined ratio by weight of approximately 1:1 of CBD to THC.

Sativex® in Cancer Pain

Cancer pain represents the initial target indication for Sativex® in the United States. The Phase III cancer pain programme is being performed in conjunction with GW’s licensing partner for Sativex® in the US, Otsuka Pharmaceutical Co. Ltd. The programme, which is fully funded by Otsuka, includes two Phase III randomised placebo-controlled multi-centre multinational trials as well as a long term extension study. Each Phase III trial will include approximately 370 patients and will evaluate the efficacy and safety of Sativex® versus placebo over a 5 week treatment period.

Cancer Pain

Studies suggest that more than one-third of patients with cancer, and more than three-quarters of those with advanced disease, have chronic pain. Large surveys indicate that optimal opioid therapy does not yield sufficient relief in a substantial proportion of these patients.

About GW

GW was founded in 1998 and listed on the AIM, a market of the London Stock Exchange, in June 2001. Operating under license from the UK Home Office, the company researches and develops cannabinoid pharmaceutical products for patients who suffer from a range of serious ailments, in particular multiple sclerosis and cancer pain. GW has assembled a large in-house scientific team with expertise in cannabinoid science as well as experience in the development of both plant-based prescription pharmaceutical products and medicines containing controlled substances. GW occupies a world leading position in cannabinoids and has developed an extensive international network of the most prominent scientists in the field. For further information, please visit www.gwpharm.com

This news release may contain forward-looking statements that reflect GWs current expectations regarding future events, including development and regulatory clearance of the GW’s products. Forward-looking statements involve risks and uncertainties. Actual events could differ materially from those projected herein and depend on a number of factors, including (inter alia), the success of the GW’s research strategies, the applicability of the discoveries made therein, the successful and timely completion of uncertainties related to the regulatory process, and the acceptance of Sativex® and other products by consumer and medical professionals.